Function

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The Function constructor creates a new Function object. In JavaScript every function is actually a Function object.

Syntax

new Function ([arg1[, arg2[, ...argN]],] functionBody)

Parameters

arg1, arg2, ... argN: Names to be used by the function as formal argument names. Each must be a string that corresponds to a valid JavaScript identifier or a list of such strings separated with a comma; for example "x", "theValue", or "a,b".
functionBody: A string containing the JavaScript statements comprising the function definition.

Description

Function objects created with the Function constructor are parsed when the function is created. This is less efficient than declaring a function with a function expression or function statement and calling it within your code, because such functions are parsed with the rest of the code.

All arguments passed to the function are treated as the names of the identifiers of the parameters in the function to be created, in the order in which they are passed.

Note: Functions created with the Function constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the Function constructor was called. This is different from using eval with code for a function expression.

Invoking the Function constructor as a function (without using the new operator) has the same effect as invoking it as a constructor.

Properties and Methods of `Function`

The global Function object has no methods or properties of its own, however, since it is a function itself it does inherit some methods and properties through the prototype chain from Function.prototype.

`Function` prototype object

Properties

Function.prototype.arguments: An array corresponding to the arguments passed to a function. This is deprecated as property of Function. Use the arguments object available within the function instead.
~~Function.arity~~: ~~Used to specifiy the number of arguments expected by the function, but has been removed. Use the length property instead.~~
Function.prototype.caller: Specifies the function that invoked the currently executing function.
Function.prototype.length: Specifies the number of arguments expected by the function.
Function.prototype.name: The name of the function.
Function.displayName: The display name of the function.
Function.prototype.constructor: Specifies the function that creates an object's prototype. See Object.prototype.constructor for more details.

Methods

Function.prototype.apply(): Calls a function and sets its this to the provided value, arguments can be passed as an Array object.
Function.prototype.bind(): Creates a new function which, when called, has its this set to the provided value, with a given sequence of arguments preceding any provided when the new function was called.
Function.prototype.call(): Calls (executes) a function and sets its this to the provided value, arguments can be passed as they are.
Function.prototype.isGenerator(): Returns true if the function is a generator; otherwise returns false.
Function.prototype.toSource(): Returns a string representing the source code of the function. Overrides the Object.prototype.toSource method.
Function.prototype.toString(): Returns a string representing the source code of the function. Overrides the Object.prototype.toString method.

`Function` instances

Function instances inherit methods and properties from Function.prototype. As with all constructors, you can change the constructor's prototype object to make changes to all Function instances.

Examples

Specifying arguments with the `Function` constructor

The following code creates a Function object that takes two arguments.

// Example can be run directly in your JavaScript console

// Create a function that takes two arguments and returns the sum of those arguments
var adder = new Function('a', 'b', 'return a + b');

// Call the function
adder(2, 6);
// > 8

The arguments "a" and "b" are formal argument names that are used in the function body, "return a + b".

A recursive shortcut to massively modify the DOM

Creating functions with the Function constructor is one of the ways to dynamically create an indeterminate number of new objects with some executable code into the global scope from a function. The following example (a recursive shortcut to massively modify the DOM) is impossible without the invocation of the Function constructor for each new query if you want to avoid closures.

<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>MDN Example - a recursive shortcut to massively modify the DOM</title>
<script type="text/javascript">
var domQuery = (function() {
  var aDOMFunc = [
    Element.prototype.removeAttribute,
    Element.prototype.setAttribute,
    CSSStyleDeclaration.prototype.removeProperty,
    CSSStyleDeclaration.prototype.setProperty
  ];

  function setSomething(bStyle, sProp, sVal) {
    var bSet = Boolean(sVal), fAction = aDOMFunc[bSet | bStyle << 1],
        aArgs = Array.prototype.slice.call(arguments, 1, bSet ? 3 : 2),
        aNodeList = bStyle ? this.cssNodes : this.nodes;

    if (bSet && bStyle) { aArgs.push(''); }
    for (
      var nItem = 0, nLen = this.nodes.length;
      nItem < nLen;
      fAction.apply(aNodeList[nItem++], aArgs)
    );
    this.follow = setSomething.caller;
    return this;
  }

  function setStyles(sProp, sVal) { return setSomething.call(this, true, sProp, sVal); }
  function setAttribs(sProp, sVal) { return setSomething.call(this, false, sProp, sVal); }
  function getSelectors() { return this.selectors; };
  function getNodes() { return this.nodes; };

  return (function(sSelectors) {
    var oQuery = new Function('return arguments.callee.follow.apply(arguments.callee, arguments);');
    oQuery.selectors = sSelectors;
    oQuery.nodes = document.querySelectorAll(sSelectors);
    oQuery.cssNodes = Array.prototype.map.call(oQuery.nodes, function(oInlineCSS) { return oInlineCSS.style; });
    oQuery.attributes = setAttribs;
    oQuery.inlineStyle = setStyles;
    oQuery.follow = getNodes;
    oQuery.toString = getSelectors;
    oQuery.valueOf = getNodes;
    return oQuery;
  });
})();
</script>
</head>

<body>

<div class="testClass">Lorem ipsum</div>
<p>Some text</p>
<div class="testClass">dolor sit amet</div>

<script type="text/javascript">
domQuery('.testClass')
  .attributes('lang', 'en')('title', 'Risus abundat in ore stultorum')
  .inlineStyle('background-color', 'black')('color', 'white')('width', '100px')('height', '50px');
</script>
</body>

</html>

Specifications

Specification	Status	Comment
ECMAScript 1st Edition (ECMA-262)	Standard	Initial definition. Implemented in JavaScript 1.0.
ECMAScript 5.1 (ECMA-262) The definition of 'Function' in that specification.	Standard
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Function' in that specification.	Standard
ECMAScript Latest Draft (ECMA-262) The definition of 'Function' in that specification.	Draft

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

Desktop
Mobile

Feature	Chrome	Firefox (Gecko)	Internet Explorer	Opera	Safari
Basic support	(Yes)	(Yes)	(Yes)	(Yes)	(Yes)

Feature	Android	Chrome for Android	Firefox Mobile (Gecko)	IE Mobile	Opera Mobile	Safari Mobile
Basic support	(Yes)	(Yes)	(Yes)	(Yes)	(Yes)	(Yes)